Nuclear Theory·nucl-th

Tuesday·February 26, 2019

18 papers—10 primary·8 cross-listed

01
Properties of a potential energy matrix in oscillator basis
Yu. A. Lashko · V. S. Vasilevsky · G. F. Filippov
Matrix elements of potential energy are examined in detail. We consider a model problem - a particle in a central potential. The most popular forms of central potential are taken up, namely, square-well potential, Gaussian, Yukawa and exponential potentials. We study eigenvalues and eigenfunctions of the potential energy matrix constructed with oscillator functions. It is demonstrated that eigenvalues coincide with the potential energy in coordinate space at some specific discrete points. We establish approximate values for these points. It is also shown that the eigenfunctions of the potential energy matrix are the expansion coefficients of the spherical Bessel functions in a harmonic oscillator basis. We also demonstrate a close relation between the separable approximation and $L^{2}$ basis (J-matrix) method for the quantum theory of scattering.
nucl-thAnnals Phys.(2019)·4 citations
02
Charm-Baryon Production in Proton-Proton Collisions
Min He🇨🇳 · Ralf Rapp🇺🇸
Recent measurements of charm-baryon production in proton-proton collisions at the LHC have found a surprisingly large yield relative to those of $D$ -mesons. We propose that this observation can be explained by the statistical hadronization model (SHM), by employing a largely augmented set of charm-baryon states beyond the current listings of the particle data group. We estimate the additional states using guidance from the relativistic quark model and from lattice QCD. Using charm- and strange-quark fugacity factors to account for the well-known suppression of heavy flavor in elementary collisions, we compute the yields and spectra of $D$ , $D_{s}$ and $Λ_{c}$ hadrons in proton-proton collisions at $s = 5$ \,TeV. Our main finding is that the enhanced feeddown from excited charm baryons can account for the $Λ_{c} / D^{0}$ ratio measured by ALICE at midrapidity, with some caveat for the forward-rapidity LHCb data. Furthermore, assuming independent fragmentation of charm quarks but with the hadronic ratios fixed by the SHM, the measured transverse-momentum ( $p_{T}$ ) spectra of $D$ -mesons and $Λ_{c}$ can also be described; in particular, the low- $p_{T}$ enhancement in the observed $Λ_{c} / D^{0}$ ratio is attributed to the enhanced feeddown from "missing" charm-baryon states. We comment on the implications of these findings for measurements of $D_{s}$ and $Λ_{c}$ in heavy-ion collisions.
nucl-thhep-exhep-phnucl-exPLB(2019)·173 citations
03
Event Shape Sorting: prospects and femtoscopy applications
Jakub Cimerman🇨🇿 · Boris Tomášik🇸🇰
We demonstrate the use of Event Shape Sorting in femtoscopy. The method allows to select events with similar distributions if hadrons in azimuthal angle. We show that also their correlation radii exhibit interesting dependence on azimuthal angle with anisotropies of different orders visible at the same time. We further demonstrate such features of the hadron distribution which can be hardly recognised by Event Shape Engineering, but shows up in Event Shape Sorting. Finally, the influence of statistical fluctuations on sorting is investigated.
nucl-thhep-phnucl-exPoS(2019)·0 citations
04
RMF models with $σ$ -scaled hadron masses and couplings for description of heavy-ion collisions below 2A GeV
K.A. Maslov🇷🇺 · D.N. Voskresensky🇷🇺
Within the relativistic mean-field framework with hadron masses and coupling constants dependent on the mean scalar field we study properties of nuclear matter at finite temperatures, baryon densities and isospin asymmetries relevant for heavy-ion collisions at laboratory energies below 2 $A$ GeV. Previously constructed (KVORcut-based and MKVOR-based) models for the description of the cold hadron matter, which differ mainly by the density dependence of the nucleon effective mass and symmetry energy, are extended for finite temperatures. The baryon equation of state, which includes nucleons and $Δ$ resonances is supplemented by the contribution of the pion gas described either by the vacuum dispersion relation or with taking into account the $s$ -wave pion-baryon interaction. Distribution of the charge between components is found. Thermodynamical characteristics on $T - n$ plane are considered. The energy-density and entropy-density isotherms are constructed and a dynamical trajectory of the hadron system formed in heavy-ion collisions is described. The effects of taking into account the $Δ$ isobars and the $s$ -wave pion-nucleon interaction on pion differential cross sections, pion to proton and $π^{-} / π^{+}$ ratios are studied. The liquid-gas first-order phase transition is studied within the same models in isospin-symmetric and asymmetric systems. We demonstrate that our models yield thermodynamic characteristics of the phase transition compatible with available experimental results. In addition, we discuss the scaled variance of baryon and electric charge in the phase transition region. Effect of the non-zero surface tension on spatial redistribution of the electric charge is considered for a possible application to heavy-ion collisions at low energies.
nucl-thastro-ph.HEhep-phEPJA(2019)·6 citations
05
Pre-processing the nuclear many-body problem: Importance truncation versus tensor factorization techniques
Alexander Tichai🇫🇷 · Julien Ripoche🇫🇷 · Thomas Duguet🇫🇷
The solution of the nuclear A-body problem encounters severe limitations from the size of many-body operators. These limitations are typically related to both the (iterative) storing of the associated tensors and to the computational time related to their multiple contractions in the calculation of various quantities of interest. However, not all the degrees of freedom encapsulated into these tensors equally contribute to the description of many-body observables. Identifying systematic and dominating patterns, a relevant objective is to achieve an \emph{a priori} reduction to the most relevant degrees of freedom via a pre-processing of the A-body problem. The present paper is dedicated to the analysis of two different paradigms to do so. The factorization of tensors in terms of lower-rank ones, whose know-how has been recently transferred to the realm of nuclear structure, is compared to a reduction of the tensors' index size based on an importance truncation. While the objective is to eventually utilize these pre-processing tools in the context of non-perturbative many-body methods, benchmark calculations are presently performed within the frame of perturbation theory. More specifically, we employ the recently introduced Bogoliubov many-body perturbation theory that is systematically applicable to open-shell nuclei displaying strong correlations. This extended perturbation theory serves as a jumpstart for non-perturbative Bogoliubov coupled cluster and Gorkov self-consistent Green's function theories. Results obtained in "small" model spaces are equally encouraging for tensor factorization and importance truncation techniques. While the former requires significant numerical developments to be applied in large model spaces, the latter is presently applied in this context and demonstrates great potential to enable high-accuracy calculations at a much reduced computational cost.
nucl-thphysics.comp-phEPJA(2019)·24 citations
06
Alpha Clustering from the Quartet Model
Dong Bai🇨🇳 · Zhongzhou Ren🇨🇳 · Gerd Röpke🇩🇪
Alpha clustering in nuclei is considered with the quartet model (QM) where four valence nucleons (the quartet) move on the top of the core (daughter) nucleus. In the QM approach, it is assumed that the intrinsic wave function of the quartet is changed from the pure cluster configuration to the shell-model configuration when it crosses some critical radius and enters into the core nucleus. The QM approach could give not only the level scheme, the electromagnetic transition, the nuclear radius, but also the alpha-cluster formation probability. Numerical results are calculated for $^{20}$ Ne, $^{44}$ Ti, and $^{212}$ Po, where a quartet moves on top of a double magic nucleus. Good agreement with experimental data and previous theoretical studies is obtained. The QM approach is a useful complement to the present phenomenological and microscopic models and could help deepen our understanding of alpha clustering across the nuclide chart.
nucl-thPRC(2019)·29 citations
07
Longitudinal conductivity of hot magnetized collisional QCD medium in the inhomogeneous electric field
Manu Kurian🇮🇳 · Vinod Chandra🇮🇳
The longitudinal current density induced by the inhomogeneous electric field in the hot magnetized quark-gluon plasma has been investigated and utilized in obtaining the conductivity of the medium. The analysis has been done in the regime where inhomogeneity of the field is small so that the collision effect could be significant. The modeling of the QCD medium is based on a quasiparticle description where the medium effects have been encoded in the effective quarks, antiquarks and gluons. The temperature dependence of the linear longitudinal current density (in terms of the electric field) and the additional components of current density due to the inhomogeneity of electric field (in terms of its derivatives) have been obtained by solving the $(1 + 1) -$ dimensional effective covariant kinetic theory with a proper collision term. The conductivity has been obtained from the current density in the presence of the inhomogeneous field. The collisional aspects of the medium have been captured by including both thermal relaxation approximation and the Bhatnagar-Gross-Krook collision kernels in the analysis. Further, the hot QCD medium effects and higher Landau level contributions to the current density and the conductivity have been investigated. It has been seen that the effects of inhomogeneity of the field and the mean field corrections to the current density and the conductivity are more visible in the temperature regions which are not far from the transition temperature.
nucl-thhep-phPRD(2019)·20 citations
08
A cranked self-consistent mean-field description of the triaxially deformed rotational bands in 138Nd
Yue Shi
The survey of different configurations near Fermi surface of 138Nd results in 12 lowest configurations, at both positive- and negative-deformations. These are calculated to be the energetically lowest configurations. The results show that, for both EDFs, the rotational states based on positive-minimum, which is at gamma~35, are lower than the respective configurations with negative-deformation. The general trends of the spin-versus-omega curve, and the energy-versus-spin curve reproduce well those of the experimental data. Further, for the observed bands `T1-T8', the calculated results using SLy4L allows the configurations of the observed bands to be assigned. The calculations predict transitional quadrupole moments, which can be used to compare with future experimental data. The current cranked self-consistent mean-field calculations of the near-yrast high-spin rotational bands in 138Nd reproduce well the experimental data. The results suggest that the experimentally observed bands can be assigned to the calculated bands with various configurations at the positive-deformation. The predictions of the current calculations are complementary to that of the well-know macroscopic-microscopic calculations, both of which await future experiment to verify.
nucl-thPRC(2019)·2 citations
09
Empirical Evidence of Isospin Memory in Compound Nuclear Fission
Swati Garg · Ashok Kumar Jain
We present empirical evidence of isospin dependence in the compound nuclear fission cross-sections and fission widths, which suggests that the compound nucleus (CN) possibly retains the memory of the isospin when it is formed. We examine the idea, first proposed by Yadrovsky [1], for three pairs of reactions where experimental data of fission cross section at various excitation energies are available. One of the pairs of reactions is the same as used by Yadrovsky i.e. $^{209}$ Bi( $p$ , f) and $^{206}$ Pb( $α$ , f) leading to the CN $^{210}$ Po but with an improved experimental data set. The other two pairs of reaction sets are, $^{185}$ Re( $p$ , f) and $^{182}$ W( $α$ , f) leading to the CN $^{186}$ Os and, $^{205}$ Tl( $p$ , f) and $^{202}$ Hg( $α$ , f) leading to the CN $^{206}$ Pb. An observable difference between the fission branching ratios in two different isospin states suggests that the CN seems to remember its isospin at the point of formation. This possibility is further supported by another method, where additional empirical evidence for four CN, viz. $^{210}$ Po, $^{209}$ Bi, $^{207}$ Bi, and $^{198}$ Hg, is obtained from the experimental data in Zhukova et al. [2]. Further, the data also suggest a possible new signature of the weakening of CN process and gradual transition to non-compound processes as the energy rises. Fresh experimental efforts as proposed, are required to confirm these findings.
nucl-th0 citations
10
Oxygen-16 Spectrum from Tetrahedral Vibrations and their Rotational Excitations
C. J. Halcrow · C. King · N. S. Manton
A reinterpretation of the complete energy spectrum of the Oxygen-16 nucleus up to 20 MeV, and partly beyond, is proposed. The underlying intrinsic shape of the nucleus is tetrahedral, as in the naïve alpha-particle model and other cluster models, and A, E and F vibrational phonons are included. The A- and F-phonons are treated in the harmonic approximation, but the E-vibrations are extended into a two-dimensional E-manifold of D2-symmetric, four-alpha-particle configurations, following earlier work. This allows for the underlying tetrahedral configuration to deform through a square configuration into the dual tetrahedron, so there is tunnelling between the tetrahedron and its dual, with the associated breaking of parity doubling. However, E-manifold states can still be interpreted in terms of E-phonons. Rotational excitations of the vibrational states are analysed as in the classic work of Dennison, Robson and others, with centrifugal corrections to the rotational energy spectrum included. States with F-phonons require Coriolis corrections too. The first-excited $0^{+}$ state at 6.05 MeV is modelled as a state with two E-phonons; this allows a good fit of the lowest $2^{+}$ and $2^{-}$ states as excitations with one E-phonon. The Coriolis parameter $ζ$ is chosen positive to ensure the right splitting of the $3^{+}$ and $3^{-}$ states near 11 MeV. Altogether, about 80 states with isospin zero are predicted below 20 MeV, and these match rather well the more than 60 experimentally tabulated states. Several high-spin states are predicted, up to spin 9 and energy 30 MeV, and these match some of the high-spin, natural parity states in this energy range that have been observed. The model proposed here is mainly phenomenological but it receives some input from analysis of Skyrmions with baryon number 16.
nucl-thIJMPE(2019)·25 citations

Affiliations

first authorsco-authorsvia INSPIRE